Tin oxide refractory and method for its production

ABSTRACT

To provide a tin oxide refractory which prevents volatilization of SnO 2  in a high temperature zone from an early stage and which also has high erosion resistance to glass. 
     A tin oxide refractory comprising SnO 2 , SiO 2  and ZrO 2  as essential components, wherein the total content of SnO 2 , SiO 2  and ZrO 2  in the tin oxide refractory is at least 70 mass %, and, based on the total content of SnO 2 , SiO 2  and ZrO 2 , the content of SnO 2  is from 32 to 98 mol %, the content of SiO 2  is from 1 to 35 mol % and the content of ZrO 2  is from 1 to 35 mol %.

TECHNICAL FIELD

The present invention relates to a tin oxide refractory, particularly toa tin oxide refractory which contains SiO₂ and ZrO₂ as essentialcomponents and which, by containing them in prescribed amounts not tosubstantially reduce the erosion resistance to glass, effectivelyprevents volatilization of SnO₂, and a method for its production.

BACKGROUND ART

A tin oxide refractory prepared by sintering a refractory compositioncontaining tin oxide (SnO₂) as the main component, has very high erosionresistance to glass, as compared with a refractory which is commonlyused, and its use as a refractory for a glass melting furnace is beingstudied.

For example, Patent Document 1 has proposed a tin oxide refractory for aglass melting furnace containing from 85 to 99 wt % of SnO₂. However, nocase has been known in which such a refractory is practically used as arefractory for a portion in contact with glass in a glass productionapparatus.

The reason is that as a basic characteristic, SnO₂ has such a naturethat it volatilizes as SnO in a high temperature zone, particularly in ahigh temperature zone of at least 1,200° C. Such volatilization isconsidered to bring about such a problem that the surface structure ofthe refractory tends to be porous and brittle, and SnO₂ itself tends topeel off, or a volatilized SnO component tends to be concentrated andcoagulated in a low temperature zone in the glass melting apparatus, sothat a SnO₂ component will fall and be included as a foreign matter inglass, thus leading to deterioration of the yield in the production of amolded product of glass.

On the other hand, a SnO₂ sintered body is used as an electrode materialfor glass melting in a high temperature zone. Usually, such a SnO₂electrode material is made of from 90 to 98 mass % of SnO₂ and fromabout 0.1 to 2.0 mass % of a sintering assistant and an agent to reduceelectrical resistance and is utilized as a material having bothproperties of high erosion resistance to molten glass and low electricalresistance sufficient for power distribution. However, such a commonSnO₂ electrode material tended to gradually volatilize as SnO in a hightemperature zone, particularly in a high temperature zone of at least1,200° C., whereby deterioration was unavoidable.

As a conventional technique to solve the problem of volatilization ofSnO₂ in a high temperature zone, Non-patent Document 1 has reported on aSnO₂ sintered body wherein 0.5 mol % of CoO as a sintering assistant isincorporated to a SnO₂ powder and from 0 to 10 mol % of ZrO₂ as avolatilization-preventing component is incorporated based on the totalcontent of ZrO₂ and SnO₂, to prevent volatilization of SnO₂.

Further, Patent Document 2 has proposed an electrode material for aglass melting furnace, wherein together with a sintering assistant andan agent to reduce electrical resistance, as a volatilization-preventingagent, a Y component being an oxide such as ZrO₂, HfO₂, TiO₂, Ta₂O₅ orCeO₂ is incorporated in an amount of from 0 to 8 mass % based on thetotal content of Y and SnO₂, to prevent volatilization of SnO₂.

These SnO₂ sintered bodies containing a volatilization-preventingcomponent have a structure having the volatilization-preventing agentsolid-solubilized inside of SnO₂ particles, and when SnO₂ volatilizes ina high temperature zone, the volatilization-preventing agentsolid-solubilized inside of SnO₂ particles will be concentrated and willprecipitate on the SnO₂ particle surface to cover the SnO₂ particlesurface, whereby it is possible to prevent volatilization of SnO₂.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-A-54-132611-   Patent Document 2: WO2006/124742

Non-Patent Document

-   Non-patent Document 1: Maitre, D. Beyssen, R. Podor, “Effect of ZrO₂    additions on sintering of SnO₂-based ceramics”, Journal of the    European Ceramic Society, 2004, Vol. 24, p. 3111-3118

DISCLOSURE OF INVENTION Technical Problem

However, the above SnO₂ volatilization-preventing component starts toprecipitate on the SnO₂ particle surface for the first time when it hasbeen concentrated in the SnO₂ particles to exceed its solid solubilitylimit concentration by volatilization of SnO₂, and therefore, at theinitial stage after beginning of volatilization of SnO₂, thevolatilization-preventing component is not sufficiently precipitated onthe SnO₂ particle surface, and an excellent volatilization-preventingeffect is not provided from the initial stage after beginning of thevolatilization. Therefore, if such a SnO₂ sintered body is used as acomponent for a long period of time, the deterioration of the componentdue to volatilization of SnO₂ is unavoidable.

Accordingly, in a case where such a SnO₂ sintered body is used for aglass production apparatus, a problem is considered to be likely tooccur such that due to brittleness of the sintered body surface, SnO₂itself tends to peel off, or a volatilized SnO component tends to beconcentrated and coagulated in a low temperature zone in the glassmelting apparatus, so that the SnO₂ component will fall and be includedas a foreign matter in glass, thus leading to deterioration of the yieldin the production of a molded product of glass.

Therefore, it is an object of the present invention to solve the aboveproblem of the prior art and to provide a tin oxide refractory whichprevents volatilization of SnO₂ in a high temperature zone from an earlystage and also has a high erosion resistance to glass, and which issuitable as a refractory for a glass production apparatus, and a processfor its production.

Solution to Problem

-   [1] A tin oxide refractory comprising SnO₂, SiO₂ and ZrO₂ as    essential components, wherein the total content of SnO₂, SiO₂ and    ZrO₂ in the tin oxide refractory is at least 70 mass %, and, based    on the total content of SnO₂, SiO₂ and ZrO₂, the content of SnO₂ is    from 32 to 98 mol %, the content of SiO₂ is from 1 to 35 mol % and    the content of ZrO₂ is from 1 to 35 mol %.-   [2] The tin oxide refractory according to above [1], wherein after    heat treatment at 1,300° C. for 350 hours, a ZrSiO₄ phase and a ZrO₂    phase are formed on the sintered body surface of the tin oxide    refractory.-   [3] The tin oxide refractory according to above [1] or [2], wherein    the total content of SnO₂, SiO₂ and ZrO₂ is at least 95 mass %.-   [4] The tin oxide refractory according to any one of above [1] to    [3], wherein, based on the total content of SnO₂, SiO₂ and ZrO₂, the    content of SnO₂ is from 76 to 98 mol %, the content of SiO₂ is from    1 to 12 mol % and the content of ZrO₂ is from 1 to 12 mol %.-   [5] The tin oxide refractory according to any one of above [1] to    [4], which further contains at least one component selected from the    group consisting of oxides of CuO, Cu₂O, ZnO, Mn₂O₃, CoO, Al₂O₃,    Sb₂O₃ and Li₂O.-   [6] The tin oxide refractory according to any one of above [1] to    [5], wherein after heat treatment at 1,300° C. under −700 mmHg for    350 hours, the volatilization rate of SnO₂ is at most ⅕ as compared    with a SnO₂ sintered body having a SnO₂ content of at least 99 mol    %.-   [7] A glass melting furnace provided with the tin oxide refractory    as defined in any one of above [1] to [6].-   [8] A method for producing a tin oxide refractory, which comprises    uniformly mixing powder raw materials, forming the mixture into a    desired shape and subjecting the formed mixture to sintering    treatment, wherein the tin oxide refractory comprises SnO₂, SiO₂ and    ZrO₂ as essential components, and as a powder raw material for the    SiO₂ and ZrO₂ components, a ZrSiO₄ powder is used.

Advantageous Effects of Invention

The tin oxide refractory of the present invention contains SnO₂ having ahigh erosion resistance to glass and ZrO₂ and SiO₂ having a high effectto prevent volatilization of SnO₂ in a high temperature zone in goodbalance, whereby it is possible to provide a highly erosion resistantrefractory which is capable of exhibiting an excellentvolatilization-preventing effect from the initial stage after beginningof volatilization of SnO₂.

Further, according to the method for producing a tin oxide refractory ofthe present invention, it is possible to obtain the above tin oxiderefractory having excellent characteristics efficiently by a simpleoperation and with a constant product quality.

DESCRIPTION OF EMBODIMENTS

The present invention is characterized in that SnO₂, SiO₂ and ZrO₂ areincorporated so that their contents in the tin oxide refractory would bein the prescribed amounts. Now, the present invention will be describedin detail.

SnO₂ to be used in the present invention has high resistance to erosionby molten glass and high heat resistance, and thus is incorporated asthe main component of the refractory.

SiO₂ to be used in the present invention is a component to form matrixglass and to provide a stress relaxation function. Further, it is acomponent having a function to prevent volatilization of SnO₂ being themain component in the refractory.

ZrO₂ to be used in the present invention is a component having highresistance to erosion by molten glass and also having a function toprevent volatilization of SnO₂ being the main component in therefractory.

In the present invention, the total content of SnO₂, SiO₂ and ZrO₂contained in the refractory is adjusted to be at least 70 mass %. Thereason is such that if other components are contained in the refractorytoo much, the content of SnO₂, SiO₂ and ZrO₂ decreases, andparticularly, the excellent erosion resistance of SnO₂ to glass tends tobe impaired. In order to bring the erosion resistance to be good, thetotal content of SnO₂, SiO₂ and ZrO₂ is preferably at least 85 mass %,more preferably at least 95 mass %. Further, the total content of SnO₂,SiO₂ and ZrO₂ is preferably from 97 to 99.5 mass %.

Further, in the present invention, when the total content of SnO₂, SiO₂and ZrO₂ being essential components is regarded to be 100 mol %, SnO₂ iscontained in an amount of from 32 to 98 mol %, SiO₂ is contained in anamount of from 1 to 35 mol %, and ZrO₂ is contained in an amount of from1 to 35 mol %.

In the present invention, by adjusting the content of SnO₂, SiO₂ andZrO₂ in the refractory to be within the prescribed range as mentionedabove, and further adjusting the relation of these components to havethe prescribed relation, it is possible to obtain a tin oxide refractorywhich prevents volatilization of SnO₂ in a high temperature zone from anearly stage and which also has high erosion resistance to glass.

As a result of a study on the contents of SnO₂, SiO₂ and ZrO₂, thepresent inventors have found that in a case where two components of SnO₂and ZrO₂ are used as the main components without incorporating SiO₂,ZrO₂ to exhibit an effect to prevent volatilization of SnO₂ is presentas solid-solubilized in SnO₂. And, the characteristics of the obtainablerefractory are influenced by the firing temperature and the temperaturelowering rate at the time of producing the refractory, but, for example,in a case where firing was carried out at 1,400° C. for 5 hours and thetemperature lowering was carried out at a rate of 300° C./hr, the solidsolubility limit concentration of ZrO₂ in SnO₂ was from about 20 to 25mol %.

Whereas, when the composition is made to contain SiO₂ as in the presentinvention, the solid solubility limit concentration of ZrO₂ in SnO₂decreases to a large extent to about 12 mol %, although the cause is notclearly understood. Therefore, in the composition range containing SiO₂,as compared with a case where only ZrO₂ is contained without containingSiO₂, at the time of volatilizing SnO₂ in a high temperature zone, ZrO₂solid-solubilized in SnO₂ reaches the solid solubility limit in an earlystage and will precipitate on the SnO₂ particle surface. Thus, itbecomes possible to exhibit an excellent effect to preventvolatilization of SnO₂ from the initial stage after beginning ofvolatilization, as compared with a case where no SiO₂ is contained.

Further, the majority of SiO₂ present in a non-crystallized state at thegrain boundary of SnO₂ having ZrO₂ solid-solubilized therein(hereinafter referred to also as SnO₂—ZrO₂ solid solution) will reactwith ZrO₂ precipitated as exceeded the solid solubility limit and willbe present as ZrSiO₄ at the grain boundary of the SnO₂—ZrO₂ solidsolution thereby to reduce the relative surface area of SnO₂. Thus, anexcellent volatilization-preventing effect over a long period of time isobtainable also as compared with a case where ZrO₂ is contained withoutcontaining SiO₂.

Further, ZrO₂ not reactive with SiO₂ is also present, and such ZrO₂exhibits a volatilization-preventing effect by itself. With respect toZrSiO₄ and ZrO₂, their presence can be confirmed by means of an electronmicroscopic device such as SEM-EDX (Scanning Electron Microscope-EnergyDispersive X-ray Detector (manufactured by Hitachi High TechnologiesCorporation, trade name: S-3000H).

Here, the solid solubility limit concentration was determined as anapproximate solid solubility limit concentration of ZrO₂solid-solubilized in SnO₂ by analyzing a sintered body structure bymeans of SEM-EDX with respect to a sintered body obtained by changingthe amount of ZrSiO₄ added.

Now, the reason for limiting the refractory in the present invention tothe above composition will be explained as follows.

As mentioned above, when the total amount of SnO₂, ZrO₂ and SiO₂ isregarded as 100 mol %; if the contents of the respective componentssatisfy the relation of from 32 to 98 mol % of SnO₂, from 1 to 35 mol %of ZrO₂ and from 1 to 35 mol % of SiO₂, the solid solubility limitconcentration of ZrO₂ decreases, and ZrO₂ starts to precipitate on theSnO₂ particle surface at an early stage after beginning ofvolatilization of SnO₂. Thus, an excellent effect to preventvolatilization of SnO₂ can be obtained from an earlier stage as comparedwith a case where no SiO₂ is contained. Further, the majority of SiO₂will react with ZrO₂ precipitated as exceeded the solid solubility limitand will be present as ZrSiO₄ at the grain boundary of the SnO₂—ZrO₂solid solution thereby to reduce the surface area of SnO₂ exposed to theexterior environment. Thus, an excellent effect to preventvolatilization of SnO₂ for a long period of time is obtainable ascompared with a case where ZrO₂ is contained without containing SiO₂.

In this composition range, ZrO₂ is mainly in a state solid-solubilizedin SnO₂, and a portion exceeding the solid solubility limit willprecipitate at the grain boundary of SnO₂. The precipitated ZrO₂ willreact with SiO₂ and will be present as ZrSiO₄ at the grain boundary ofthe SnO₂—ZrO₂ solid solution. However, depending upon the amount of SiO₂present, unreacted one will be partially present as ZrO₂ at the grainboundary of the SnO₂—ZrO₂ solid solution.

SiO₂ reacts with SnO₂, ZrO₂ and other components and is present in anon-crystallized state at the grain boundary of a SnO₂—ZrO₂ solidsolution, and when ZrO₂ precipitates at the grain boundary, it willreact with ZrO₂ to form ZrSiO₄.

As described above, the tin oxide refractory of the present inventionexhibits an excellent effect to prevent volatilization of SnO₂, becausefrom an early stage in volatilization of SnO₂, the solid solubilityamount of ZrO₂ in SnO₂ reaches the solid solubility limit concentration,and ZrSiO₄ and ZrO₂ are formed on the SnO₂ surface of the sintered body.

According to the tin oxide refractory of the present invention, forexample, after heat treatment at 1,300° C. for 350° C., on the sinteredbody surface, a ZrSiO₄ phase and a ZrO₂ phase are formed. Further, in acase where the SiO₂ content is at least about 5 mol % based on the totalamount of SnO₂, ZrO₂ and SiO₂, a SiO₂ phase also remains. Thus, if suchhigh temperature treatment is done before use, it is possible to produceand use a refractory capable of exhibiting an excellentvolatilization-preventing effect immediately after use.

At that time, if the content of SiO₂ is small at a level of less than 1mol % based on the total content of SnO₂, ZrO₂ and SiO₂, a phenomenon ofdecrease in the solid solubility limit concentration of ZrO₂ in SnO₂will not be observed, and development of the volatilization-preventingeffect in the initial stage after beginning of volatilization of SnO₂tends to be delayed to a certain extent, and since the SiO₂ content issmall, even if ZrO₂ precipitates, formation of ZrSiO₄ will be less,whereby improvement in the volatilization-preventing effect will besmall.

If the content of ZrO₂ is small at a level of less than 1 mol % based onthe total content of SnO₂, ZrO₂ and SiO₂, the volatilization-preventingeffect by ZrO₂ and ZrSiO₄ will be very small.

If the content of SiO₂ is large at a level of exceeding 35 mol % basedon the total content of SnO₂, ZrO₂ and SiO₂, the content of SiO₂ is toomuch, whereby the content of SnO₂ tends to be small, and the erosionresistance to glass tends to decrease.

If the content of ZrO₂ is large at a level of exceeding 35 mol % basedon the total content of SnO₂, ZrO₂ and SiO₂, the content of ZrO₂ is toomuch, whereby the content of SnO₂ tends to be small, and the erosionresistance to glass tends to decrease.

Here, in the tin oxide refractory of the present invention, the contentof ZrO₂ is preferably within a range of from 1 to 12 mol % based on thetotal content of SnO₂, ZrO₂ and SiO₂. Further, the content of SiO₂ isalso preferably within a range of from 1 to 12 mol % based on the totalcontent of SnO₂, ZrO₂ and SiO₂. Accordingly, the content of SnO₂ ispreferably within a range of from 76 to 98 mol % based on the totalcontent of SnO₂, ZrO₂ and SiO₂.

Further, irrespective of the above conditions, sintering treatment iscarried out usually by heat treatment at from 1,200 to 1,600° C. forfrom 3 to 5 hours. Therefore, depending upon the sintering conditions inactual treatment, the blend amounts of SnO₂, ZrO₂ and SiO₂ in therefractory composition may be adjusted.

Further, the above-mentioned other components are not particularlylimited so long as they are ones not to impair the characteristics asthe refractory of the present invention, and they may be knowncomponents which are used in tin oxide refractories.

Such other components may, for example, be oxides such as CuO, Cu₂O,ZnO, Mn₂O₃, CoO, Li₂O, Al₂O₃, TiO₂, Ta₂O₅, CeO₂, CaO, Sb₂O₃, Nb₂O₅,Bi₂O₃, UO₂, HfO₂, etc.

It is preferred to contain, among these oxides, at least one oxideselected from the group consisting of CuO, ZnO, Mn₂O₃, CoO, Al₂O₃, Sb₂O₃and Li₂O. Further, CuO, ZnO, Mn₂O₃, CoO, Li₂O or the like effectivelyserves as a sintering assistant. If such a sintering assistant isincorporated, the strength of the refractory may be more improved, forexample, as densified by firing at 1,400° C. for 5 hours. Accordingly,it is more preferred to contain at least one oxide selected from thegroup consisting of CuO, ZnO, Mn₂O₃, CoO and Li₂O, and particularlypreferred to contain CuO.

A preferred tin oxide refractory of the present invention is arefractory wherein after heat treatment at 1,300° C. under −700 mmHg for350 hours, the volatilization rate of SnO₂ is at most ⅕ as compared witha SnO₂ sintered body having a SnO₂ content of at least 99 mol %. At thattime, the comparison is carried out by adjusting the open porositydifference between them to be at most 1%. Here, the open porosity iscalculated by a known Archimedes method.

The tin oxide refractory of the present invention may be produced byuniformly mixing powder raw materials, forming the mixture into adesired shape and subjecting the formed mixture to sintering treatmentat a high temperature of at least 1,200° C., preferably from 1,300 to1,450° C. More specifically, fine powder raw materials are weighed inrequired amounts so that the components in the obtainable refractorywould be in the above-mentioned contents, e.g. the components such SnO₂,SiO₂, ZrO₂, CuO, etc. would be in the prescribed blend amounts, and putin a rotary ball mill or a vibration ball mill, followed by mixing andpulverization by the pulverizer using an organic solvent such as ethanolas a medium. The obtained slurry is dried under reduced pressure,followed by press molding by means of metallic mold pressing orisostatic pressing, and the obtained molded product is sintered, forexample, at 1,400° C. for 5 hours, to obtain a tin oxide refractory.

The raw materials are not limited to the above-mentioned combination ofpowders, and for example, a ZrSiO₄ powder may be used as a raw materialfor ZrO₂ and SiO₂ being volatilization-preventing components.

Further, a powder of a simple substance metal such as Zr, Si or Cu, ametal salt compound containing such a metal, Zr(OH)₂, CuZrO₃, CuCO₃, orCu(OH)₂ may, for example, be used. Among them, CuZrO₃ or CuCO₃ ispreferred.

In a case where a ZrSiO₄ powder is used as a raw material for ZrO₂ andSiO₂ being volatilization-preventing components, within a range whereinthe solid solubility amount of ZrO₂ in SnO₂ is at most 12 mol %, SnO₂serves as a dissociation accelerator of ZrSiO₄, and therefore, forexample, by firing at 1,400° C. for 5 hours, it is possible to letZrSiO₄ be dissociated to ZrO₂ and SiO₂, thereby to produce a tin oxiderefractory of the present invention.

Further, in the case where a ZrSiO₄ powder is used as a raw material, itis not necessary, for example, to put raw material powders of ZrO₂ andSiO₂ dividedly into a mixing apparatus, whereby the production processcan be simplified. Further, mixing of the raw material powders issimplified, and a uniform mixture is obtainable, which contribute toshortening of the production process and stability of the productquality.

EXAMPLES

Now, the present invention will be described specifically with referenceto Examples and Comparative Examples, but it should be understood thatthe present invention is by no means restricted by such descriptions.

Ex 1 to 26

Firstly, as raw materials for producing tin oxide refractories, powderraw materials having average particle sizes, chemical components andpurities as shown in Table 1 were prepared. Then, so that a tin oxiderefractory would have a composition as shown in Table 2, powders ofSnO₂, ZrO₂, SiO₂, ZrSiO₄, Al₂O₃, Sb₂O₃, CuO, Mn₂O₃, etc. were blended inthe proportions as shown in Table 3.

In Table 2, in Ex (Ex 1, 2, 4 to 6, 11 to 17, 23 and 25) wherein themolar ratio of ZrO₂ to SiO₂ is 1:1, a ZrSiO₄ powder was used. Whereas,in Ex wherein the molar ratio of ZrO₂ to SiO₂ is not 1:1, a ZrO₂ powderand a SiO₂ powder were used.

TABLE 1 Raw material powder Purity, mass % Average particle size μm SnO₂99.0 2.7 ZrO₂ 99.9 0.1 SiO₂ 99.9 4.0 ZrSiO₄ 99.5 1.1 Al₂O₃ 99.9 0.3Sb₂O₃ 99.9 1.1 CuO 99.9 1.0 Mn₂O₃ 99.9 5.1 Li₂O 99.0 3.0 ZnO 99.9 1.0

TABLE 2 Content [mol %] based on (SnO₂ + SiO₂ + ZrO₂) Composition [mol%] SnO₂ SiO₂ ZrO₂ SnO₂ ZrO₂ SiO₂ Al₂O₃ CuO Mn₂O₃ Li₂O ZnO Sb₂O₃ CaO Na₂Ocontent content content Ex 1 95.1 2.0 2.0 0.0 0.9 0.0 0.0 0.0 0.0 0.00.0 96.0 2.0 2.0 Ex 2 89.1 5.0 5.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 89.95.0 5.0 Ex 3 69.1 5.0 25.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 69.7 25.2 5.0Ex 4 75.1 12.0 12.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 75.8 12.1 12.1 Ex 563.1 18.0 18.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 63.7 18.2 18.2 Ex 6 49.125.0 25.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 49.5 25.2 25.2 Ex 7 56.1 25.018.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 56.6 18.2 25.2 Ex 8 85.1 2.0 12.00.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 85.9 12.1 2.0 Ex 9 79.1 2.0 18.0 0.0 0.90.0 0.0 0.0 0.0 0.0 0.0 79.8 18.2 2.0 Ex 10 71.1 10.0 18.0 0.0 0.9 0.00.0 0.0 0.0 0.0 0.0 71.7 18.2 10.1 Ex 11 89.1 5.0 5.0 0.0 0.0 0.9 0.00.0 0.0 0.0 0.0 89.9 5.0 5.0 Ex 12 75.1 12.0 12.0 0.0 0.0 0.9 0.0 0.00.0 0.0 0.0 75.8 12.1 12.1 Ex 13 79.1 5.0 5.0 10.0 0.9 0.0 0.0 0.0 0.00.0 0.0 88.8 5.6 5.6 Ex 14 69.1 5.0 5.0 20.0 0.9 0.0 0.0 0.0 0.0 0.0 0.087.4 6.3 6.3 Ex 15 88.6 5.0 5.0 0.0 0.9 0.0 0.0 0.0 0.5 0.0 0.0 89.9 5.15.1 Ex 16 87.6 5.0 5.0 0.0 0.0 0.0 2.4 0.0 0.0 0.0 0.0 89.8 5.1 5.1 Ex17 89.1 5.0 5.0 0.0 0.0 0.0 0.0 0.9 0.0 0.0 0.0 89.9 5.0 5.0 Ex 18 99.10.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 100.0 0.0 0.0 Ex 19 94.1 0.0 5.00.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 95.0 5.0 0.0 Ex 20 95.1 4.0 0.0 0.0 0.90.0 0.0 0.0 0.0 0.0 0.0 96.0 0.0 4.0 Ex 21 74.1 25.0 0.0 0.0 0.9 0.0 0.00.0 0.0 0.0 0.0 74.8 0.0 25.2 Ex 22 59.1 5.0 35.0 0.0 0.9 0.0 0.0 0.00.0 0.0 0.0 59.6 35.3 5.0 Ex 23 29.1 35.0 35.0 0.0 0.9 0.0 0.0 0.0 0.00.0 0.0 29.4 35.3 35.3 Ex 24 57.1 40.0 2.0 0.0 0.9 0.0 0.0 0.0 0.0 0.00.0 57.6 2.0 40.4 Ex 25 49.1 5.0 5.0 40.0 0.9 0.0 0.0 0.0 0.0 0.0 0.083.1 8.5 8.5 Ex 26 0.0 0.0 1.3 92.6 0.0 0.0 0.0 0.0 0.0 0.5 5.6 0.0100.0 0.0

TABLE 3 Composition [mass %] Total content of SnO₂, SiO₂ and SnO₂ ZrO₂SiO₂ Al₂O₃ CuO Mn₂O₃ Li₂O ZnO Sb₂O₃ CaO Na₂O ZrO₂ in refractory [mass %]Ex 1 97.0 1.7 0.8 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 2 93.1 4.3 2.10.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 3 82.7 4.9 11.9 0.0 0.5 0.0 0.00.0 0.0 0.0 0.0 99.5 Ex 4 83.3 10.9 5.3 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.099.5 Ex 5 73.9 17.2 8.4 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 6 61.425.6 12.5 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 7 66.7 24.3 8.5 0.00.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 8 92.5 1.8 5.2 0.0 0.5 0.0 0.0 0.00.0 0.0 0.0 99.5 Ex 9 89.5 1.9 8.1 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5Ex 10 81.8 9.4 8.3 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 11 92.7 4.22.1 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 12 82.9 10.8 5.3 0.0 0.0 1.00.0 0.0 0.0 0.0 0.0 99.5 Ex 13 85.6 4.4 2.2 7.3 0.5 0.0 0.0 0.0 0.0 0.00.0 92.2 Ex 14 77.5 4.6 2.2 15.2 0.5 0.0 0.0 0.0 0.0 0.0 0.0 84.3 Ex 1592.1 4.3 2.1 0.0 0.5 0.0 0.0 0.0 1.0 0.0 0.0 98.4 Ex 16 92.9 4.3 2.1 0.00.0 0.0 0.7 0.0 0.0 0.0 0.0 99.3 Ex 17 93.1 4.3 2.1 0.0 0.0 0.0 0.0 0.50.0 0.0 0.0 99.5 Ex 18 99.5 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5Ex 19 97.4 0.0 2.1 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 20 96.2 3.30.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 21 78.0 21.5 0.0 0.0 0.5 0.00.0 0.0 0.0 0.0 0.0 99.5 Ex 22 76.2 5.3 18.0 0.0 0.5 0.0 0.0 0.0 0.0 0.00.0 99.5 Ex 23 40.4 39.7 19.4 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 2462.7 35.9 0.9 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 99.5 Ex 25 59.4 5.0 2.432.7 0.5 0.0 0.0 0.0 0.0 0.0 0.0 66.8 Ex 26 0.0 0.0 0.8 94.9 0.5 0.0 0.00.0 0.0 0.3 3.5 0.8

The blended raw material powders were mixed and pulverized for 48 hoursby means of a rotary ball mill (trade name: AN-3S, manufactured by AichiElectric Co., Ltd.) using ethanol (400 ml) as a medium, whereupon theobtained slurry was dried under reduced pressure and formed into amolded product by isostatic pressing (the pressing machine wasmanufactured by Nikkiso Co., Ltd., trade name: CL15-28-20) with 1,500kg/cm². The obtained molded product was held at 1,400° C. for 5 hours inthe atmospheric air atmosphere for firing and then cooled at a rate of300° C./hr to obtain a tin oxide refractory.

A test piece having a diameter of 15 mm and a height of 5 mm was cut outfrom a part of the obtained tin oxide refractory and heat-treated at1,300° C. in an environment of −700 mmHg for from 10 to 400 hours,whereby the mass reduction in each case was measured (using GH-252,trade name, manufactured by A & D Company, Limited), and thevolatilization amount (unit: mg) and the volatilization rate (unit:mg/hr) were calculated.

Further, a test piece of 15 mm×25 mm×50 mm(vertical×horizontal×lengthwise) cut out from the obtained tin oxiderefractory was immersed in soda lime glass (trade name: Sun Green VFL,manufactured by Asahi Glass Company Limited) at 1,300° C. for 100 hoursin the atmospheric air atmosphere, whereupon the erosion degree wasmeasured, and the erosion resistance was investigated.

The data of the volatilization rate and the erosion degree obtained asdescribed above are summarized in Table 4.

TABLE 4 Volatilization rate After 10 hr of After 350 hr of Erosiondegree heat treatment heat treatment (1,300° C., 100 hr) Ex 1 15 7.6 11Ex 2 10.5 4 12 Ex 3 12.6 7.1 14 Ex 4 14.7 1.6 11 Ex 5 10.4 1.3 12 Ex 620.4 9.3 16 Ex 7 13.6 5.7 14 Ex 8 36.9 3.6 11 Ex 9 37.7 3 15 Ex 10 16.86.7 14 Ex 11 14.2 5.8 12 Ex 12 11.5 4.9 12 Ex 13 18.7 6.2 17 Ex 14 20.26.5 19 Ex 15 11.2 5.1 15 Ex 16 37.6 7.9 15 Ex 17 20.1 4.2 9 Ex 18 100100 11 Ex 19 167.7 113 11 Ex 20 55.3 13.1 13 Ex 21 47.3 11.9 8 Ex 2221.2 7.3 30 Ex 23 30.5 11.5 33 Ex 24 40.1 8.8 29 Ex 25 22.3 4.9 35 Ex 260 0 100

In Tables 2 to 4, Ex 1 to 17 are Examples of the present invention, andEx 18 to 26 are Comparative Examples.

The erosion resistance to glass in each of Examples and ComparativeExamples was compared with the alumina fused cast brick (trade name:MB-G, manufactured by AGC Ceramics Co., Ltd.) in Ex 26 which is widelyused in glass production apparatus and was represented by an erosiondegree relative to the maximum erosion depth being 100, of the erodedportion after the erosion test of MB-G.

Further, the volatilization rate in each of Ex 1 to 17 and Ex 18 to 26was represented by a volatilization rate relative to the volatilizationrate being 100 after the test piece in Ex 18 was heat-treated at 1,300°C. in an environment of −700 mmHg for 10 hours and 350 hours. Here, asthe respective volatilization rates after the heat treatment for 10hours and 350 hours, an average volatilization rate per unit surfacearea calculated from the mass reduction during the heat treatment timeof from 0 hour to 10 hours, and an average volatilization rate per unitsurface area calculated from the mass reduction during the heattreatment time of from 350 hours to 400 hours, are relatively shown.

Further, the open porosity of each sample was measured by an Archimedesmethod, and in each case, a sample with 1.0% or less was used.

Ex 18 represents a tin oxide sintered body having a compositionexcluding ZrO₂ and SiO₂, whereby the erosion resistance to glass issubstantially equal to Ex 1 to 17, but since novolatilization-preventing component is contained, the volatilizationrate of SnO₂ is very fast.

Ex 19 represents a tin oxide sintered body having a compositionexcluding ZrO₂, whereby the erosion resistance to glass is substantiallyequal to Ex 1 to 17, but since no ZrO₂ as a volatilization-preventingcomponent is contained, the volatilization rate of SnO₂ is very fast.

Ex 20 and 21 represent a tin oxide sintered body having a compositionexcluding SiO₂, whereby the erosion resistance to glass is substantiallyequal to Ex 1 to 17, but since no SiO₂ is contained, the solidsolubility limit concentration of ZrO₂ in SnO₂ is high. Further, thecontent of ZrO₂ as a volatilization-preventing component is small,whereby it takes time till ZrO₂ reaches the solid solubility limitconcentration by volatilization of SnO₂, and the volatilization rate ofSnO₂ after 10 hours of heat treatment is faster than in Ex 1 to 17.Further, since no SiO₂ is contained, also after 350 hours of heattreatment, the volatilization rate of SnO₂ is faster as compared with Ex1 to 17.

Ex 22 represents a tin oxide sintered body having a composition whereinthe amount of SiO₂ is increased, whereby the volatilization rate issubstantially equal to Ex 1 to 17, but since the content of SnO₂ issmall, the erosion resistance to glass is lower than in Ex 1 to 17.

Ex 23 represents a tin oxide sintered body having a composition whereinthe amounts of ZrO₂ and SiO₂ are increased, whereby the volatilizationrate is substantially equal to Ex 1 to 17, but since the content of SnO₂is small, the erosion resistance to glass is lower than in Ex 1 to 17.

Ex 24 represents a tin oxide sintered body having a composition whereinthe amount of ZrO₂ is increased, whereby the volatilization rate issubstantially equal to Ex 1 to 17, but since the content of SnO₂ issmall, the erosion resistance to glass is lower than in Ex 1 to 17.

Ex 25 represents a tin oxide sintered body having a composition whereinAl₂O₃ is incorporated as other component, whereby the volatilizationrate is substantially equal to Ex 1 to 17, but since the content of SnO₂is small, the erosion resistance to glass is lower than in Ex 1 to 17.

Ex 26 represents an alumina fused cast brick (trade name: MB-G,manufactured by AGC Ceramics Co., Ltd.), whereby no volatilizationoccurs, but the erosion resistance to glass is lower than in Ex 1 to 17.

On the other hand, Ex 1 to 17 representing Examples of the presentinvention present results such that the volatilization rate and theerosion resistance to glass are better as compared with Ex 18 to 26.From these evaluation results, it has been made clear that as comparedwith the tin oxide refractories in Comparative Examples, the tin oxiderefractories in Examples of the present invention are excellent tinoxide refractories each being highly effective to prevent volatilizationof SnO₂ and having a high erosion resistance to glass, with a goodbalance of both physical properties.

INDUSTRIAL APPLICABILITY

The tin oxide refractory of the present invention is excellent inerosion resistance to glass and capable of effectively preventingvolatilization of SnO₂ and thus is suitable as a refractory for a glassmelting furnace.

This application is a continuation of PCT Application No.PCT/JP2012/083928, filed on Dec. 27, 2012, which is based upon andclaims the benefit of priority from Japanese Patent Application No.2011-289690 filed on Dec. 28, 2011. The contents of those applicationsare incorporated herein by reference in their entireties.

What is claimed is:
 1. A tin oxide refractory comprising SnO₂, SiO₂ andZrO₂ as essential components, wherein the total content of SnO₂, SiO₂and ZrO₂ in the tin oxide refractory is at least 70 mass %, and, basedon the total content of SnO₂, SiO₂ and ZrO₂, the content of SnO₂ is from76 to 98 mol %, the content of SiO₂ is from 1 to 12 mol % and thecontent of ZrO₂ is from 1 to 35 mol %, and wherein when heat treatmentat 1,300° C. for 350 hours is conducted, a ZrSiO₄ phase and a ZrO₂ chaseare formed on a sintered body surface of the tin oxide refractory. 2.The tin oxide refractory according to claim 1, wherein the total contentof SnO₂, SiO₂ and ZrO₂ is at least 95 mass %.
 3. The tin oxiderefractory according to claim 1, wherein, based on the total content ofSnO₂, SiO₂ and ZrO₂, the content of ZrO₂ is from 1 to 12 mol %.
 4. Thetin oxide refractory according to claim 1, further comprising at leastone component selected from the group consisting of CuO, Cu₂O, ZnO,Mn₂O₃, CoO, Al₂O₃, Sb₂O₃ and Li₂O.
 5. The tin oxide refractory accordingto claim 1, wherein after heat treatment at 1,300° C. under −700 mmHgfor 350 hours, a volatilization rate of SnO₂ is at most ⅕ as comparedwith a SnO₂ sintered body having a SnO₂ content of at least 99 mol %.